1. Field of the Invention
The present invention relates to a planar light source device.
2. Description of the Prior Art
Liquid crystal displays (LCD) or other flat display devices are non-self-illumination displays, wherein backlight modules are included for generating area light. The backlight modules can be categorized into two types: a top view type and a side view type. A prior art top view type backlight module of an LCD includes cold cathode fluorescent lamps (CCFL), a diffuser, a prism sheet, etc. In order to uniformly distribute light for providing a proper planar light source for the LCD, distances between light sources and between light sources, the diffuser, and the prism sheet have to be controlled precisely to avoid the problem of non-uniform illumination. Besides the components of the above mentioned top view backlight module, a prior art side view backlight module of an LCD further includes a light guide plate for spreading light. However, it still cannot solve the problem of non-uniform illumination. Furthermore, the backlight modules of the two types are complicated and cause the problems of high manufacturing costs and complex assembly.
In order to overcome the above-mentioned problems, a side view light-emitting diode disclosed in TW Patent Publication No. 541726 includes a light-emitting diode package and a lens. The lens guides the light emitted from the LED package to become a planar side view light before the light guide plate guides the light. However, the side view light-emitting diode is still so complicated that the manufacture cost is still a problem.
A backlight module disclosed in TW Patent Publication No. 575722 includes a plurality of linear light sources (such as tubes), or a plurality of point light sources (such as light-emitting diodes), a light guide plate, and optical multiplayer films (such as diffusers and prism sheets). The light guide includes a plurality of grooves at the bottom thereof for accommodating the tubes and a plurality of cuts at the top thereof corresponding to the grooves for diffusing the light emitted from the tubes through the light guide plate by means of total internal reflection. However, the above mentioned backlight module can be utilized only for a monochromatic light source. If the white light for the backlight source is formed by mixing point light sources of different colors (e.g. red, green, and blue light-emitting diodes), the backlight source of the backlight module causes the problem of the non-uniform color mixing or a partially converging problem. Besides, the manufacture cost and the difficulty in assembly is still a problem.